The Department of Transportation lowered the boom on Southwest Airlines yesterday for allegedly violating rules on airfare advertising—slapping the no-frills line with a $200,000 penalty for hawking ticket prices that were literally too good to be true. Since Southwest is a repeat offender, the DOT said it was adding an extra $100,000 to the airline’s total fine from an earlier penalty that it had partly forgiven. In the latest case, the airline got into trouble when it advertised $59 fares from Atlanta to New York, Los Angeles, and Chicago as part of a fare sale last October. The dirt-cheap deal proved to be illusory when DOT investigators attempted to purchase tickets at those prices.

Southwest, in its defense, said that advertising those fares to the three cities was an “inadvertent error,” made only in the audio portion of TV commercials that aired in Atlanta; discount fares to other cities in those same spots were legitimate, it said. “The sale provided significant savings to consumers in Atlanta and across the country—with more than 300,000 consumers saving millions of dollars,” Southwest said.

But that argument isn’t likely to sway regulators in Washington, who are getting increasingly aggressive at cracking down on airline gimmicks that border on bait-and-switch tactics. It comes at a time when a major battle is shaping up in the capital over all manner of airline practices.

As we reported earlier, the House of Representatives is considering a bill aimed at undoing the DOT’s two-year-old, full-fare ad rule, which requires airlines to display prominently the full cost of a ticket with all mandatory taxes and fees included. (The airlines say it’s unfair to force them, but not other suppliers like hotels, to bold face the total tab.) But the administration’s going in the other direction, charging ahead with even more rules the airlines won’t like. The latest, released for public comment last week, would require airlines, travel agents, and other ticket sellers such as online search sites to disclose fees for all the items they sell—including checked baggage, early seat selection and boarding privileges, and other so-called ancillary services. While most websites selling air travel do offer this information, the DOT said it’s “difficult to determine when searching for air travel,” and, accordingly, “many consumers are unable to understand the true cost of travel.”

The rule also includes a number of other reforms, such as requiring all airlines, not just the largest ones, to report on-time performance, and stats on bumping and mishandled baggage. It also expands the definition of the term “ticket agent” to include online sites like Kayak and Google that offer flight search tools; they too would have to spell out all required information to the traveling public.

Judging from the comments filed so far, DOT has struck a nerve; more than 200 have weighed in so far and the deadline isn’t until August 21. “Airlines have been fooling passengers long enough with their fees,” said one typical commenter. You can add your two cents at regulations.gov (docket DOT-OST-2014-0056).